The present invention relates to the field of pulse-echo ultrasound imaging systems which are used with probes which are inserted into or through body tissue and maneuvered so that a selected portion of that probe is within the imaged area. Aspiration biopsy is one example of such a procedure.
In aspiration biopsy, a small, hollow needle is inserted directly into the body to a desired point, whereupon a tissue sample is withdrawn, such as by vacuum aspiration. The needle is then withdrawn, but because of its relatively insignificant diameter, wound closure occurs normally by muscular and tissue tension, generally without the need for sutures, cauterization, or the like. For optimal effectiveness, aspiration biopsy techniques require that the tip of the needle be precisely accurately placed at the location of the tissues to be sampled. When properly performed, these techniques are safe, effective, and minimally traumatic.
Other common diagnostic and therapeutic procedures involving the manuevering of a probe through body tissues include various catheterization procedures. In these procedures, a catheter is maneuvered through a vein, artery, or other duct to a desired internal location. Such procedures include arterial angioplasty, thrombus removal, bile duct clearage, etc.
Various radiological (i.e. X-ray fluoroscopic) techniques have been utilized for ascertaining or estimating the location of tissue to be treated, sampled or diagnosed, and for aiding in the maneuvering of a given probe to its desired body location. These radiological techniques not only suffer from dimensional/accuracy limitations, but also from other inherent drawbacks related to the radiation doses involved in performing such procedures.
More recently, a variety of ultrasound imaging techniques have been suggested, particularly for in vivo imaging of relatively deep soft body tissue. Such ultrasound techniques include conventional A-mode, B-mode, and C-mode approaches. Because of their superior imaging capability with minimal hazard or risk to the patient, such techniques have achieved prominent use, particularly for needle location during aspiration biopsy techniques.
In one class of prior art aspiration biopsy systems, exemplified by U.S. Pat. Nos. 3,721,227 (Larson et al.), 4,108,165 (Copp et al.), 4,029,084 (Soldner), and German Pat. No. 42 55 401 (Vindenskaber), a biopsy needle is inserted in the center of an ultrasound transducer or transducer array, parallel to the direction of propagation of the ultrasound energy, so that the biopsy needle shows on the ultrasound image only if it diverts from such parallel orientation.
In another class of prior art systems, exemplified by U.S. Pat. No. 4,058,114 (Soldner), the biopsy needle is carried by angular aiming apparatus which in turn is mechanically coupled to a pointer overlying the ultrasound image field. As the needle angle is established, the pointer overlays the image and follows the progress of the needle.
In yet another class of prior art systems, exemplified by U.S. Pat. Nos. 3,556,079 (Omizo) and 4,429,539 (Vilkomerson at al.), a transducer element at the skin and another one within or at the tip of the needle correspond with one another to precisely locate the needle in the image field. In such systems, the needle is normally insertable into the body at an angle and in a direction which is completely independent from the angle and the position of the pulse-echo ultrasound imaging system. Accordingly, while such systems are effective at imaging the needle once the tip is disposed within the ultrasonically illuminated scan plane (imaging field), difficulties may be encountered in locating the needle in the scan plane for illumination and imaging.
These prior art systems have experienced a certain degree of commercial success, and are normally effective for their intended uses. Perhaps the least efficient of these systems are those which require parallel orientation of the propagating ultrasound energy and the needle, because of their failure to yield either clear composite images or accurate needle depth representation. While the systems of U.S. Pat. No. 4,429,539 (Vilkomerson et al.) are among the most effective, such systems do generally require special electronics and compact, expensive transducer elements which are mountable at the needle tip and removable through the biopsy needle.